Fluid ink jet systems typically include one or more print heads having a plurality of ink jets from which drops of fluid are ejected toward a print medium. The ink jets of a print head receive ink from an ink supply chamber (manifold) in the print head which, in turn, receives ink from a source such as an ink reservoir or an ink cartridge. Each ink jet includes a channel having one end in fluid communication with the ink supply manifold. The other end of the ink channel has an orifice or nozzle for ejecting drops of ink. The nozzles of the ink jets may be formed in an aperture plate that has openings corresponding to the nozzles of the ink jets. During operation, drop ejecting signals activate actuators to expel drops of fluid from the ink jet nozzles onto the print medium. By selectively activating the actuators to eject ink drops as the print medium and print head assembly are moved relative to one another, the deposited drops can be precisely patterned to form particular text and/or graphic images on the print medium.
Conventional ink jet print heads such as solid ink jet (SIJ) print heads can be constructed using stainless steel aperture plates with nozzles which are etched chemically or formed mechanically. The stainless steel aperture plate can be coated, for example with polytetrafluoroethylene (PTFE), to reduce wetting of the aperture plate by the ink. Decreased wetting assists in proper jetting of ink away from the print head by reducing adhesion of the ink to the print head as it is being ejected from the nozzle, and can result in a self-cleaning print head and improved print quality.
Conventional stainless steel aperture plates for ink jet print heads are expensive to manufacture, for example due to the required formation of apertures or nozzles within the stainless steel substrate using chemical or mechanical etch techniques. A polymer aperture plate which uses, for example, a polyimide substrate can be less expensive to manufacture, for example because the nozzles can be laser etched to reduce processing time and costs. Either a stainless steel aperture plate or a polymer aperture plate can be coated with an oleophobic coating, which is an anti-wetting material such as PTFE which can result in improved print quality.
Another feature which can be formed over the aperture plate to reduce wetting is referred to as a reentrant structure or an overhang structure. A particular method of forming a plurality of reentrant structures is described in U.S. patent application Ser. No. 12/648,004, filed Dec. 28, 2009, commonly assigned herewith and incorporated herein by reference in its entirety. Reentrant structures can include a plurality of protrusions over the front (external) surface of the aperture plate. Each protrusion can include a pillar or stem formed from a first layer which is topped by a cap which overhangs the pillar and is formed from a second layer. The reentrant structures can be formed on the substrate itself, or on an oleophobic layer which coats the substrate. The aperture plate can thus include the substrate, the oleophobic layer, and the plurality reentrant structures.
A method of forming a print head having improved performance and lower cost than conventional print heads would be desirable.